This invention is directed to a gettering system which permits the achievement of high vacuum in a permanantly sealed dewar for a long dewar life-time. The high vacuum is achieved by employing two getters, one of which is principally for water adsorption, and the other for light gas adsorption, with the two getters being closely related so that they can both be heated for activation during low temperature dewar baking and vacuum pumpout.
High vacuum devices such as certain lamps, electromagnetic tubes and the like, can be permanently sealed off and commonly retain a very high vacuum for long periods of time. This is achieved primarily by virtue of the fact that during manufacture and final evacuation the entire vacuum envelope is baked at high temperature to drive off water and other gas contaminants which are on the inner surfaces of the package. Following closure of the vacuum package, a small internal gettering device may be used to absorb any subsequent out-gassing that may take place in the package.
There is a considerable amount of prior art in gettering because it was an early problem in vacuum devices such as incandescent lights and radio vacuum tubes. MacRae U.S. Pat. No. 1,623,351 and Lockwood U.S. Pat. No. 2,449,786 are directed to early types of gettering structures. Lockwood discloses the use of a zirconium-aluminum getter material on filament support wires. Lester U.S. Pat. No. 2,117,735 and King U.S. Pat. No. 2,183,841 disclose multiple materials in the getter for different purposes. Barosi U.S. Pat. No. 4,146,497 has a considerable background on gettering materials, and particularily at adsorptive gettering materials. The entire disclosure of that patent is incorporated herein by this reference for background discussion. It is principally directed to an open cell metallic support for a zirconium-graphite getter material.
However, in specialized applications, high temperature baking may not be possible. This is particularily true in some dewar packages of refrigerated infrared detection devices where high temperature baking during the final evacuation may cause damage to some of the components in the infrared detection device. This in turn means that the burden for removal of gas and water contaminants is largely placed on the internal gettering devices. Previous such devices have not been fully capable of achieving the desired and required gettering.